The present invention is an advance in the art of delivery systems for the gradual release of active agents. This invention enables an active agent to be gradually released through the direct interaction of the agent and a solvent either within channels in the structure enclosing the active agent or through exposure of the active agent to the solvent when the structure enclosing the active agent is deformed or through diffusion of the active agent through the wall material.
Prior to the present invention, the gradual release of active agents, such as drugs, could be accomplished by the diffusion of the active agent through an encapsulating material. A discussion of such encapsulated structures is found in R. Dunn & D. Lewis, Fibrous Polymers for the Delivery of Contraceptive Steroids to the Female Reproductive Tract, Controlled Release of Pesticides and Pharmaceuticals 125-46 (D. Lewis ed. 1981), which describes fiber-like structures. Alternatively, an encapsulating shell around the active agent could be ruptured causing exposure of the active agent to various solvents.
Melt blending is another technique that was used prior to the present invention to obtain a mixture of active agent and support material to form a gradual release structure. In melt blending a polymer and an active agent are mixed and melted together. This molten mixture is then cast and solidified. The solidified mixture could then be ground or otherwise shaped for its intended end use. The present invention provides benefits over melt blending techniques by reducing the processing steps required with that technique and reducing the time that the active agent is exposed to heat during processing.